The ultra-refractory carbides, ZrC, HfC and TaC, thanks to the interstitial nature of their structure that leads to a combination of metallic, covalent and ionic bonds, exhibit the physical properties of ceramics and the electronic properties of metals, i.e., high hardness and strength with high thermal and electrical conductivities. The relatively recent discovery and implementation of sintering aids has significantly eased the processing conditions required to produce dense, fine-grain-size UHTCs with desirable sets of properties [1] and has ignited interest in the more widespread use of these materials in a wide range of applications, among others Generation IV very high temperature nuclear reactors (VHTRs ) and solar absorbers in novel high-temperature concentrating solar power systems. An additional challenge to fully exploit the potential of UHTCs is to develop methods that allow smaller and more simply produced components to be integrated into more complex and potentially multimaterial structures, as effective processes for joining these materials to themselves, other ceramics, or metals. TLP bonding of ceramics allows to join high-temperature, high-performance materials at significantly reduced temperatures and with shorter cycles relative to brazing and solid-state diffusion bonding [2]. In the present study, the use of a Ni/Nb/Ni interlayer, which exhibits many desirable features for TLP bonding, was explored to join pure ZrC, HfC and TaC by executing a short bonding cycle under low load in a high-vacuum furnace. Microstructural and microchemical analyses of the resulting joints were conducted using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). It was shown that the interactions of the interlayer with the UHTC have an important influence on the liquid volume and composition, the path of phase evolution, the final microstructure and the joint properties. On successful joints, results of nanoindentation tests and flexural strength experiments are shown. [1] D. Sciti, S. Guicciardi and M. Nygren, "Spark plasma sintering and mechanical behaviour of ZrC-based composites", Scripta Materialia, 59, [6], 638-41 (2008). [2] J. D. Sugar, J. T. McKeown, S. Hong, T. Akashi, K. Nakashima and A. M. Glaeser, "Transient-Liquid-Phase and Liquid-Film-Assisted Joining of Ceramics," Journal of the European Ceramic Society, 26, [4-5], 363-72 (2006).
Transient-Liquid-Phase Bonding of UHTCs Using Refractory-Metal-Based Interlayers
L Esposito;L Silvestroni;
2012
Abstract
The ultra-refractory carbides, ZrC, HfC and TaC, thanks to the interstitial nature of their structure that leads to a combination of metallic, covalent and ionic bonds, exhibit the physical properties of ceramics and the electronic properties of metals, i.e., high hardness and strength with high thermal and electrical conductivities. The relatively recent discovery and implementation of sintering aids has significantly eased the processing conditions required to produce dense, fine-grain-size UHTCs with desirable sets of properties [1] and has ignited interest in the more widespread use of these materials in a wide range of applications, among others Generation IV very high temperature nuclear reactors (VHTRs ) and solar absorbers in novel high-temperature concentrating solar power systems. An additional challenge to fully exploit the potential of UHTCs is to develop methods that allow smaller and more simply produced components to be integrated into more complex and potentially multimaterial structures, as effective processes for joining these materials to themselves, other ceramics, or metals. TLP bonding of ceramics allows to join high-temperature, high-performance materials at significantly reduced temperatures and with shorter cycles relative to brazing and solid-state diffusion bonding [2]. In the present study, the use of a Ni/Nb/Ni interlayer, which exhibits many desirable features for TLP bonding, was explored to join pure ZrC, HfC and TaC by executing a short bonding cycle under low load in a high-vacuum furnace. Microstructural and microchemical analyses of the resulting joints were conducted using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). It was shown that the interactions of the interlayer with the UHTC have an important influence on the liquid volume and composition, the path of phase evolution, the final microstructure and the joint properties. On successful joints, results of nanoindentation tests and flexural strength experiments are shown. [1] D. Sciti, S. Guicciardi and M. Nygren, "Spark plasma sintering and mechanical behaviour of ZrC-based composites", Scripta Materialia, 59, [6], 638-41 (2008). [2] J. D. Sugar, J. T. McKeown, S. Hong, T. Akashi, K. Nakashima and A. M. Glaeser, "Transient-Liquid-Phase and Liquid-Film-Assisted Joining of Ceramics," Journal of the European Ceramic Society, 26, [4-5], 363-72 (2006).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
